1. Field of the Invention
This invention relates to a holder system for turbidity sensors of the type used in machines for cleansing articles. Systems of this type, generally, allow the turbidity of the liquid fluid employed in the cleansing of the articles to be accurately measured without affecting the performance capacity of the sensor.
2. Description of the Related Art
Reducing the amount of energy consumed by a machine for cleansing articles, such as a clothes washer or a dishwasher, is a significant problem, in part because of increasing energy costs. In such machines, the amount of energy consumed is primarily determined by the amount of energy needed to heat the water used to wash the articles. Thus, decreased water consumption for such machines may result in a significant and permanent energy efficiency.
Appliances for cleansing articles, such as dishwashers, are typically preprogrammed to perform a complete washing operation in a predetermined number of wash cycles, each wash cycle having a predetermined duration. A wash cycle may comprise the separate operation steps of providing substantially particle-free water into a tub of the cleansing machine (fill cycle), circulating the water during the wash cycle (circulation cycle), and draining or flushing the soiled water from the tub after the water is used to wash the articles (drain cycle). Usually, though, the machine user may only select from the limited number of preprogrammed options. Such preprogramming does not use energy efficiently because the machine often performs a large number of wash cycles, each cycle lasting for an excessive duration, to assure that cleanliness of the articles is achieved. To improve the energy efficiency of such machines, closed loop feedback control has been introduced. Several techniques are available to indirectly monitor cleanliness of the articles during closed loop feedback control of the appliance including use of a device for measuring the turbidity of the liquid used to wash the articles.
Devices for measuring turbidity that detect the transmission of coherent light or other suitable form of electromagnetic radiation propagated through the liquid used to wash the articles have been employed to ascertain information about the progress of the wash. However, these devices are not ideal for use in household appliances. Such devices are often times difficult or non-economical to implement due to the complex electronic circuitry necessary to perform the complex turbidity measurements. Furthermore, such devices are subject to measurement error. Factors such as cleansing liquid turbulence, cloudiness of the liquid sample chamber, light source dimming, or device performance degradation may cause attenuation of the amount of light detected and thus, affect measurement accuracy. The precision of such devices is also not entirely satisfactory. This imprecision has the additional effect of making turbidity measurements provided by such devices difficult to interpret in a closed loop feedback control system.
As disclosed in U.S. Pat. No. 5,259,219, herein incorporated by reference, the location of the sensor is also of importance. For instance, the above referred application discloses how to solve problems generally associated with dishwashers wherein the sensor is located either in the overhead spray arm hose where water is being fed into the machine or in the drain hose where the soiled water or effluent is being drained from the machine. In either of these two instances, the turbulence of the cleansing liquid adversely affects the performance characteristics of the sensor because bubbles that are created by the liquid turbulence may provide a false read in the sensor. This is because the bubbles affect the light measuring characteristics of the sensor.
Although the foregoing allowed patent application discloses a turbidity sensor holder which is capable of efficiently and advantageously measuring the turbidity of the liquid used in cleansing the articles, it is desirable to improve the capability for collecting samples of the cleansing liquid. For instance, the sensor holder system disclosed therein uses liquid collecting holes through a tub wall to collect samples of the cleansing liquid, i.e., water. In this approach the quantity of water collected is dependent on the wettability of the tub wall, that is, the collection of liquid samples in the system depends on how well the water flows along the tub wall as the water droplets run down the tub wall. In general, tub wall materials such as plastics are typically hydrophobic in nature which causes the water droplets to bead. When the water droplets form beads, these beads generally flow bypassing the collecting holes rather than into the holes. A number of approaches, which generally have not been entirely satisfactory due to various detrimental factors, can be used to improve the wettability of the tub wall. For instance, an inner surface of the tub wall can be coated with a hydrophilic material or the inner surface of the tub wall along which the water droplets run down can be chemically treated by a suitable oxidation process to improve its wettability. In each case, the coating or the oxidation treatment imposes manufacturing processes which add to the cost and complexity of the washing machine. Further, either the surface coating or the surface treatment typically wears out with age and usage with the possibility of changing the surface appearance after a relatively short period of time. In addition, it is desirable to provide venting provisions for allowing air to escape from a reservoir of the sensor holder as the reservoir fills with the cleansing liquid to be sampled in a manner that such air is neither obstructed by the cleansing liquid nor by particulates in the cleansing liquid.
It is apparent from the foregoing that there exists a need in the art for a turbidity sensor holder with improved capability for collecting samples of the liquid used in cleansing the articles, and which eliminates the need to provide a coating on the tub wall surface or to chemically alter such tub wall surface. It is a purpose of this invention to fulfill these and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.